The present invention relates to a scroll compressor of the type used for an air compressor or a refrigerating or air-conditioning compressor, and, more specifically, the invention relates to a double scroll compressor having scroll wraps on both sides of an end plate.
To increase the capacity of a scroll compressor, a so called double scroll compressor has heretofore been proposed, which includes an orbiting scroll having spiral scrolls on both sides of an end plate and stationary scrolls each having a scroll was which is formed in a spiral shape to mesh with the corresponding one of the wraps of the orbiting scroll. In such a double scroll compressor, the amount of heat generated by a compressed gas remarkably increases as a result of an increase in capacity, as compared with ordinary single scroll compressors.
Incidentally, the art of effectively radiating the heat generated in a scroll wrap portion to improve the reliability of a conventional single scroll compressor is set forth in, for example, Japenese Patent Laid-Open No. 341384/1994. Regarding the above-described double scroll compressor, Japanese Patent Laid-Open No. 103151/1995 states that fins are provided on an orbiting scroll portion to cope with an increase in the amount of hear generated by an operating gas in a scroll wrap portion.
It is difficult to increase the capacity of a scroll compressor by increasing its scroll diameter or wrap height, because of certain limitations, such as the orbiting speed and the strength the scroll member. For this reason, a double scroll compressor has been proposed in which ordinary single scroll compressors are combined in a back-to-back fashion to realize an increase in capacity. For example, in a large scroll compressor whose driving motor output is in a 7.5-kW class, a sandwich structure is adopted in which scroll wraps are respectively disposed on both sides of the end plate of an orbiting scroll and the two scroll wraps of the orbiting scroll are meshed with the respective scroll wraps of two stationary scrolls. If the scroll compressor is constructed in this manner, the pressures of the operating gas which act in the thrust directions of a scroll wrap portion, i.e., thrust forces, act in directions opposite to each other and work to cancel themselves. This leads to the advantage that little consideration needs to be paid to the thrust forces which represent an important problem in the ordinary single scroll compressor. However, in the double scroll compressor, the orbiting scroll is sandwiched between the two stationary scrolls, so that the orbiting scroll is positioned inside the compressor and so it is difficult for the heat generated by the compressed gas to radiate from the orbiting scroll. Therefore, if heat radiating fins are simply provided on an orbiting scroll and a stationary scroll, as in the single scroll compressor disclosed in Japanese Patent Laid-Open No. 341384/1994, the structure for introducing the driving power required for the orbiting scroll becomes complicated and location in which to provide the fins are limited, and so heat radiation from the orbiting scroll becomes insufficient.
In the double scroll compressor set forth in Japanese Patent Laid-Open No. 103151/1995, although a multiplicity of cooling fins are arranged on the end plate of the orbiting scroll, no satisfactory consideration is given to ways of improving the reliability of the double scroll compressor by effectively cooling the central portion of the scroll wrap portion, which is heated to a maximum temperature in the scroll compressor. Furthermore, in the double scroll compressor set forth in Japanese Patent Laid-Open No. 103151/1995, since two auxiliary crank shafts are incorporated, in addition to a driving shaft, for the purpose of facilitating the driving of the orbiting scroll, it is difficult to form a cooling-medium flow passage which has a small fluid resistance.